One REST API for real-time voice
Create agents, attach your own carrier numbers, place calls, and read transcripts, over a small and predictable REST surface. Bearer auth, webhook events, custom functions and pagination. Flat $0.08 a minute, no credits.
{
"name": "Front desk",
"prompt": "You book appointments.",
"voice": "lucy"
}{
"id": "agent_8fk2",
"name": "Front desk"
}A small surface, laid out plainly
The API does not sprawl. A handful of resource groups cover the whole lifecycle of a voice agent, each with predictable verbs. You can read the entire surface in one sitting and know where everything lives.
POST /v1/agentsGET /v1/agentsPUT /v1/agents/:idDELETE /v1/agents/:idCreate and manage agent templates: prompt, voice, language, behaviour.
POST /v1/phone-numbersPATCH /v1/phone-numbers/:numberAttach your own carrier numbers to an agent and configure them.
POST /v1/calls/outboundPOST /v1/calls/batchGET /v1/callsPlace single or batch calls; read history with transcript and analysis.
POST /v1/smsGET /v1/keysSend messages and manage the API keys your integration uses.
Auth in one header
Every request carries a bearer token of two halves joined by a colon. The first half identifies the key, the second is the secret, and keys are created and rotated through the API so you can revoke access without disturbing your agents or numbers.
Authorization: Bearer nxf_live:nxfs_live
Events pushed to your server
Instead of polling, register a webhook and receive events as a call moves: call.started, call.in_progress, and call.ended with the full transcript, a summary and a sentiment score attached. Every call is also available from GET /v1/calls with limit and offset, so you can reconcile history at your own pace.
Plain REST, honest about the SDK
There is no SDK to install first. Nixflex is a REST API you call from any language with the HTTP client you already have, and typed client libraries are on the roadmap rather than shipped today. We would rather give you an honest surface than a thin wrapper, so what you see in the docs is exactly what you send.
Read the complete reference in the docs, or the Webhooks and Function calling pages. Coming from another platform? Nixflex is a modern alternative to Retell, Vapi and Bland. Compare them →
Developer FAQ
How do I authenticate API requests?
Every request carries a bearer token made of two halves joined by a colon: Authorization: Bearer nxf_xxx:nxfs_xxx. The first half identifies the key, the second is the secret. Keys are created and rotated through the API, so you can revoke a key without touching your agents or numbers.
What are the main endpoints?
They group cleanly: /v1/agents to create and manage agent templates, /v1/phone-numbers to attach your carrier numbers, /v1/calls/outbound and /v1/calls/batch to place calls, GET /v1/calls to read history with transcripts and analysis, plus /v1/sms and /v1/keys. It is a small, predictable surface rather than a sprawl.
Is there an official SDK?
Not yet. The API is plain REST, so you call it from any language with your existing HTTP client, and typed client libraries are on the roadmap. The endpoints and payloads in the docs are exactly what you send, with no wrapper to learn or get out of date.
How do webhooks work?
Register a URL and Nixflex posts events to it as calls happen: call.started, call.in_progress, and call.ended with the full transcript, a summary and a sentiment score. It is push-based, so you react to events instead of polling to ask whether a call has finished.
Can I paginate call and agent lists?
Yes. GET /v1/calls and GET /v1/agents accept limit and offset, so you can page through history rather than being capped at the first set of rows. The response is a plain array, which keeps existing readers working as the API grows.
Can the agent call my own API during a call?
Yes. Custom functions let the agent make an HTTP request to your endpoint mid-conversation, to look something up or trigger an action, and use the JSON you return to keep talking. Anything that has to be exact is supplied by the engine rather than left to the model.
What does the API cost?
A flat $0.08 per minute of voice, pay-as-you-go, premium model included, with your own carrier underneath. No credits, no per-endpoint charges, and no monthly platform fee to start.
Start calling the API today
Create a key, create an agent, and place your first call in minutes.